1. Statement of the Technical Field
The inventive arrangements relate generally to methods and apparatus for providing voltage conversion, and more particularly efficient variable DC to DC voltage conversion in a small volume.
2. Description of the Related Art
Conversion of a first DC voltage to second DC voltage has always been problematic. Unlike AC voltages that can be efficiently stepped up or down using simple transformers, circuits for converting DC voltages are generally more complex. Such systems tend to occupy a large volume, have noise problems, and/or operate relatively inefficiently. For example, one approach for solving the DC to DC conversion problem is the DC-AC-AC-DC converters. In such systems, a DC voltage is first converted to an AC voltage, then stepped up or down using conventional AC transformer techniques, and finally converted back to DC. This approach is relatively expensive and requires transformers that can add weight and bulk to a design.
Buck and Boost type switching converters can also be used for DC voltage conversion. However, each of these designs also suffers from problems. Pulsating input currents in Buck converters tend to send too much noise back to the source. Also, these devices tend to suffer from poor line regulation. Similarly, pulsating output currents with Boost converters are known to result in noise problems.
Another approach that has been used to solve the DC to DC conversion problem makes use of a Single-Ended Primary Inductance Converter (SEPIC). However, the SEPIC device also tends to suffer from noise problems. Further, these converters can suffer from reduced efficiencies at lower voltages. Accordingly, there is a need for compact variable DC to DC voltage conversion system that efficiently converts DC voltages with low noise and good isolation.
Homopolar machines are well known in the art. For example, several variations of such machines are described in U.S. Pat. No. 5,530,309 to Weldon, U.S. Pat. No. 5,481,149 to Kambe, U.S. Pat. No. 5,587,618 to Hathaway. These patents describe the use of a homopolar generator for producing high current, low voltage energy for various applications. U.S. Pat. No. 6,051,905 to Clark describes a homopolar machine for use in conjunction with storage batteries for an electric car. In general, however, such references have not applied homopolar machines to the problem of converting one DC voltage to a second DC voltage.
U.S. Pat. No. 5,821,659 to Smith describes a homopolar transformer for conversion of electrical energy. However, the device is mechanically complex and therefore relatively unsuited for micro-electronic fabrication on a substrate.
The invention concerns a method and device that makes use of a homopolar machine for converting a first DC voltage to a second DC voltage. According to the method, the invention can include the steps of applying a first DC voltage between an inner and outer radial portion of a primary conductive disc comprising a rotor to produce an electric current, applying a magnetic field aligned with an axis of the rotor to induce a rotation of the rotor about the axis responsive to the electric current, and coupling the rotation of the rotor to at least one secondary conductive disc disposed in the magnetic field to produce at least a second DC voltage between an inner and outer radial portion of the secondary conductive disc or discs.
The method can also include the step of controlling a ratio of the first DC voltage to the second DC voltage by selectively controlling the strength of the magnetic field applied to at least a portion of one of the conductive discs. Alternatively, or in addition thereto, the method can comprise the step of controlling a ratio of the first DC voltage to the second DC voltage by selectively controlling a radial spacing between the inner and outer radial portions of the secondary conductive disc or discs relative to the spacing between the inner and outer radial portion of the primary conductive disc.
The method can be carried out by axially aligning the secondary conductive disc or discs with the primary conductive disc, and coupling the rotation of the rotor to the secondary conductive discs, for example through a common axle. The magnetic field can be applied by positioning at least one permanent magnet adjacent to the rotor. Alternatively, or in addition thereto the magnetic field can be applied by positioning one or more electromagnets adjacent to the rotor. A ratio of the first DC voltage to the second DC voltage can be controlled by selectively controlling an electric current applied to the electromagnets.
According to one aspect of the invention, a different intensity magnetic field can be selectively applied outside a perimeter of a smaller one of the conductive discs as compared to inside the perimeter so as to control a ratio of the first DC voltages to the second DC voltage or voltages.
The invention can also include a device, for example a micro-electromechanical device for converting a first DC voltage to a second DC voltage or voltages. The device can include a primary conductive disc rotatably mounted to a rotor support structure. DC voltage input leads can be provided integrated with the substrate and coupled to a primary set of brushes for applying the first DC voltage between an inner and outer radial portion of the primary conductive disc to produce an electric current. A magnetic field source is provided for producing a magnetic field aligned for causing a rotation of the primary conductive disc responsive to the electric current. One or more secondary conductive discs is mechanically coupled to the primary conductive discs for rotation responsive to the rotation of the primary conductive disc. A diameter of the primary conductive disc can be the same size or different size as compared to a diameter of the secondary conductive disc(s). An insulator preferably electrically isolates the primary and secondary conductive discs. The secondary conductive disc(s) can also be disposed within the magnetic field for generating the second DC voltage responsive to the rotation. DC voltage output leads are provided coupled to secondary set of brushes forming an electrical connection to an inner and outer radial portion of the secondary conductive disc. If the device is formed as a micro-electromechanical device, the substrate can be a ceramic or semiconductor material.
The magnetic field is aligned parallel with an axis of rotation for each of the primary and secondary conductive discs. According to one aspect of the device, the primary and secondary conductive discs can have a common axis of rotation. According to another aspect of the invention, the magnetic field for at least a portion of one of the primary and secondary conductive discs can have an intensity that is different as compared to an intensity field applied to the other one of the primary and secondary conductive discs.
A control circuit can be provided coupled to the magnetic field source for selectively controlling the intensity of the magnetic field applied respectively to at least a portion of each of the conductive discs. For example, the control circuit can control a current applied to an electromagnet for controlling the field intensity.